The present invention relates to the control of internal combustion engines. More specifically, the present invention relates to methods and apparatus to provide for the control of a variable displacement internal combustion engine.
Present regulatory conditions in the automotive market have led to an increasing demand to improve fuel economy and reduce emissions in present vehicles. These regulatory conditions must be balanced with the demands of a consumer for high performance and quick response in a vehicle. Variable displacement internal combustion engines (ICEs) provide for improved fuel economy and torque on demand by operating on the principal of cylinder deactivation. During operating conditions that require high output torque, every cylinder of a variable displacement ICE is supplied with fuel and air (also spark, in the case of a gasoline ICE) to provide torque for the ICE. During operating conditions at low speed, low load and/or other inefficient conditions for a variable displacement ICE, cylinders may be deactivated to improve fuel economy for the variable displacement ICE and vehicle. For example, in the operation of a vehicle equipped with an eight cylinder ICE, fuel economy will be improved if the ICE is operated with only four cylinders during low torque operating conditions by reducing throttling losses. Throttling losses, also known as pumping losses, are the extra work that an ICE must perform to pump air around the restriction of a relatively closed throttle plate and pump air from the relatively low pressure of an intake manifold through the ICE and out to the atmosphere. The cylinders that are deactivated will not allow air flow through their intake and exhaust valves, reducing pumping losses by forcing the ICE to operate at a higher throttle plate angle and a higher intake manifold pressure. Since the deactivated cylinders do not allow air to flow, additional losses are avoided by operating the deactivated cylinders as xe2x80x9cair springsxe2x80x9d due to the compression and decompression of the air in each deactivated cylinder.
Previous variable displacement ICEs suffered from driveability issues created by their control systems. A transition in a previous variable displacement eight cylinder ICE to six or four cylinder operation created noticeable torque disturbances that affected the operation of the vehicle. These torque disturbances were generally considered undesirable by consumers.
The inability to control throttle position as a function of displacement in previous variable displacement ICEs contributed to the problem of torque disturbances. Previous variable displacement ICEs were equipped with conventional pedal-throttle-wire couplings that required different pedal positions for the operation of a fully displaced ICE and a partially displaced ICE. The amount of air flow through the throttle required to generate the same torque for a fully displaced and partially displaced operation was different, requiring the physical position of the throttle plate and accelerator pedal to also be different in the various operating configurations for a variable displacement ICE. Accordingly, the amount of movement in the accelerator pedal required to change the amount of torque for a fully displaced and partially displaced engine was also different. These differences in accelerator pedal operation, to generate the same torque for different modes of operation for a previous variable displacement engine, were nuisances to the operator of the vehicle.
The introduction of new engine control devices such as electronic throttle control (ETC), engine controllers, position sensors for pedal controls, and other electronics has enabled tighter control over more functions of an ICE. It is an object of the present invention to provide a variable displacement whose operation is transparent to the operator of a vehicle.
The present invention includes methods and apparatus that allow the operation of a vehicle with a variable displacement engine to be transparent to a vehicle operator. In the preferred embodiment of the present invention, an eight-cylinder internal combustion engine (ICE) may be operated as a four-cylinder engine by deactivating four cylinders. The cylinder deactivation occurs as a function of load or torque demand by the vehicle. An engine or powertrain controller will determine if the ICE should enter four-cylinder mode by monitoring the load and torque demands of the ICE. If the ICE is in a condition where it is inefficient to operate with the full complement of eight cylinders, the controller will deactivate the mechanisms operating the valves for the selected cylinders and also shut off fuel (and possibly spark in the case of a gasoline engine) to the cylinders. The deactivated cylinders will thus function as air springs to reduce pumping losses.
The transition between eight cylinders to four cylinders or four cylinders to eight cylinders will create changes in the air flow through the throttle plate into the ICE that also affect the torque output of the ICE. The method and apparatus of the present invention uses ETC and control of spark advance/retard to maintain the same engine torque during the cylinder deactivation and reactivation processes for the variable displacement ICE. Correct implementation and integration of the control schemes will allow for a seamless transition from all cylinders firing (reactivation) to half the cylinders firing (deactivation) without a torque disturbance.